P1/P2/P3 - Energy

Energy

Ability to do work

System

An object or group of objects interacting

Examples of a system

An apple sitting on a table

What happens when a system is in equilibrium

nothing changes and so nothing happens

Unit of energy

Joules (J)

Open system

allows the exchange of energy and matter to or from its surroundings

Closed system

Can exchange energy but not matter to or from its surroundings

Isolated system

Doesn’t allow the transfer of matter or energy to or from its surroundings

Conservation of energy

Energy can not be created or destroyed but can be transferred

Kinetic energy

Energy in a moving object

Gravitational potential energy

Energy in an object that is lifted above the ground

Elastic potential energy

Energy in a stretched object

Magnetic energy

Energy in a magnetic field or when two magnets interact

Chemical energy

Energy released in chemical reactions/Energy in batteries/food/fuels

Nuclear energy

Atomic nuclei release energy from their nuclear store during nuclear reactions

Thermal energy

Energy stored in a heated object

Ways energy is transferred

• Mechanically

• Electrically

• By heating

• By radiation

Mechanical transfer

When a force acts on an object (eg - pulling/pushing)

Electrical transfer

Current moving through potential difference

Heating transfer

Energy transferred from hotter object to colder one

Heating by radiation transfer

Energy transferred by electromagnetic waves

Energy transfer in an object being projected upwards

• Person holding ball has energy in their chemical store

• As ball thrown, chemical energy → Kinetic energy as it heads upwards

• As height increases, kinetic energy → Gravitational energy

Energy transfer of vehicle slowing down

• Kinetic energy as the vehicle moves

• As it decelerates, energy → Thermal energy of surroundings

• Energy is transferred due to friction between brakes and brake pads/Tyres on the ground

• Energy transferred by heating as sound waves transfer energy away from the system

What happens to KE energy store if an object speeds up and slows down

Speeds up → Energy transferred to KE

Slows down → Energy transferred away from KE

Formula for Kinetic Energy

Ke = ½ x m (Kg) x v² (m/s)

Formula for gravitational potential energy

E = m (kg) x g (N/Kg) x h (m)

Gravity on Earth

9.8N/kg

Energy changes in a stretched spring

work is done on the spring which results in energy being transferred to the elastic potential store of the spring

Energy changes in a spring being released

Energy transferred away from its elastic energy

Elastic energy formula (J)

E = ½ x k (N/m) x e²(m)

Spring Extension formula (m)

Final length - Original length

Specific heat capacity

The amount of energy required to raise the temperature of 1 kg of a substance by 1 °C

Specific heat capacity formula J/Kg °C

c= E(J)/m (kg) x ∆θ (°C)

If a substance has a low specific heat capacity

Heats and cools down quickly as it takes less energy to change its tempreature

If a substance has a high specific heat capacity

Heats and cools down slower as it takes more energy to change its temperature

If a substance has a low specific heat capacity

Heats and cools down quickly as there is less energy to change its temperature

Specific heat capacity of water

4200J/Kg °C

Two states that specific heat capacity is used in

Solids and liquids

Why copper and lead are good conductors of heat

They have a low specific heat capacity

Why water is good for heating homes

It has a high specific capacity (4200 degrees celsius)

Power

Energy transferred per unit time or Work done per unit time

Formula for power (W)

P = E (J)/t (s)

Importance of power ratings

Tells us how fast energy is being transferred from one store to another

1W =

1J/s

Conservation of energy

Energy can not be created or destroyed but can be transferred from one store to another

What the conservation of energy means

• Energy in a closed system stays constant

• Energy can be transferred from store to store usefully to do work

• Energy can dissipate to the surroundings

Conservation of energy in a bat hitting a ball

Useful: Ke of bat → Ke of ball

Wasted: Ke of bat → Thermal store of ball/bat/surroundings

Conservation of energy in an electric heater

Useful: Thermal store of heating element → Thermal store of air in room

Wasted: Thermal store of heating element → Thermal store of surroundings

Useful energy

The energy that is transferred from store to store and used for an intended purpose

Wasted energy

The energy that is not useful for the intended purpose and is dissipated to the surroundings

Ways of reducing energy loss

• Reduce amount of unwanted energy that is produced

• Preventing energy from dissipating

Ways of reducing amount of unwanted energy produced

• Lubrication

• Insulation

Lubrication

Helps reduce friction between the rubbing parts of the vehicle (eg parts of the cycle)

Insulation

Prevents the dissipation of wasted energy then less energy would be needed to replace the wasted energy

Effectiveness of insulation depends on

• How well insulation conducts heat

• Thickness of insulation

Conduction

Conduction is the process of heat being directly transmitted through a material or a substance when there is a temperature difference

Thermal conductivity

a measure of a material’s ability to conduct heat

High thermal conductivity vs Low thermal conductivity

Materials that have a high thermal conductivity heat up faster than materials with low thermal conductivity

Examples of materials with high thermal conductivity

• Diamond

• Aluminium

• Graphite

Examples of materials with low thermal conductivity

• Air

• Steel

• Bronze

Insulator

a substance that doesn't readily allow heat (or sound) to travel through it. It is a poor conductor of heat and electricity

Uses of insulator

To contain heat or sound such as keeping a house warm or building a soundproof room

energy transfer through a layer of insulating material depends on:

• Temperature difference across the material → Greater temp difference, more conduction

• Thickness of material → Difficult for heat to conduct through thicker material

• Thermal conductivity of material → Heat conducts better in materials with high thermal conductivity

Good insulators

Low thermal conductivity → Prevents transmission of heat/sound

As thick as possible → Prevents transmission of heat/sound

Insulating homes

• Loft insulation

• Cavity wall insulation

• Aluminium foil between a radiator

• Double glazed windows

• Thicker bricks

Loft insulation

Made of glass fibres or fibreglass which is a reinforced plastic material composed of woven material with glass fibres laid across and held together. It traps the air in it so reduces the rate of energy transfer making it a good insulator

Cavity wall insulation

Cavity of outer walls of house is the space between the bricks that make up the wall. It traps the air in small pockets reducing the rate of energy transfer making it a good insulator

Aluminium foil between radiator panel and wall

Reflects radiation away from the wall reducing rate of energy transfer by radiation

Double glazed windows

Have two glass panes with dry air on it or a vacuum between the panes. The thick windows are a good insulator as it reduces the rate of energy transfer. The dry air is a good insulator so it reduces rate of energy transfer. A vacuum reduces rate of energy transfer by convection

Thicker bricks of a building

Thicker bricks means it will be difficult for heat to transmit through the material hence reducing the rate of energy transfer from the inside to the outside which can help with heating costs

Efficiency

The ratio of the useful output power or energy transfer from a system to its total input power or energy transfer

Efficiency formula (%)

Useful energy output (J)/Total energy input (J) x 100

High vs low efficiency

High → Most energy transferred is useful

Low → Most energy transferred is wasted

Machines waste energy due to

• Friction between moving parts

• Air resistance

• Electrical resistance

• Sound

Reducing friction

• Add bearings to prevent components from directly rubbing against each other

• Lubrication

Reducing electrical reisstance

• Lower current

• Using components with lower resistance

Reducing air resistance

• Streamline the shapes of objects

Reducing noise

• Tightening loose parts

• Lubrication

Renewable energy resource

An energy resource that is replenished at a faster rate than the rate at which it is being used

Renewable sources

• Solar energy

• Wind

• Bio-fuel

• Hydroelectricity

• Geothermal

• Tidal

Solar energy

Photovoltaic cells using light from the sun to create electricity

Advantages/disadvantages of solar energy

Advantages → Produces no greenhouse gases/pollution, Good for making energy in remote areas

Disadvantages → Not reliable in places where there is not a lot of sun, takes up most land in farms

Wind energy

Moving wind turbines to create electricity

Advantages/Disadvantages of wind energy

Advantages → Produce no greenhouse gases/Pollution, Land can still be used for farming

Disadvantages → Not reliable, Turbines are visually unappealing

Biofuel

Plant matter, ethanol, methane can be produced and used as a fuel in place of fossil fuels

Advantages/Disadvantages of biofuel

Advantages → CO₂ produced while burning the fuel is balanced by the CO₂ absorbed whilst producing it

Disadvantages → Takes up a lot of land, consumes resources that are needed for food production

Hydroelectricity

Uses GPE of water stored in reservoirs to turn turbines which produce electricity

Advantages/Disadvantages of hydroelectricity

Advantages → Reliable, produce large amount of energy at short notice, no pollution/greenhouse gases produced

Disadvantages → Can create flooding, destroy wildlife habitat

Geothermal energy

Heat from underground to create steam which spins turbines that create electricity

Advantages/Disadvantages of Geothermal energy

Advantages → Reliable, stations are relatively small

Disadvantages → Can release harmful gases from underground, not many places are suitable

Tidal waves

Dam used to trap seawater at high tide, which is then released through a turbine creating electricity

Advantages/Disadvantages of tidal waves

Advantages → Large amount of energy produced at regular intervals, tides are predictable

Disadvantages → Very few locations available, cause environmental harms to estuaries and ships

Fossil fuels

Remains of animals/plants which are burned and then produce steam which turn turbines to make electricity

Advantages/Disadvantages of fossil fuels

Advantages → Reliable, Produce large amount of energy at short notice (short start up time)

Disadvantages → Produce greenhouse gases/pollution

Nuclear energy

Energy released from the nucleus, the core of atoms and reacting nuclear fuel creating steam that produces electricity

Advantages/Disadvantages of nuclear energy

Advantages → Reliable, produces no greenhouse gases, large amounts of energy produced from small amounts of fuel

Disadvantages → Produces dangerous radioactive waste that takes thousands of years to decay

Reliable energy resource

A resource that produces energy at any time

Non reliable resource

Energy resource that only produces energy at certain times

Ways using cleaner technologies are used

• Government grants encouraged investment of wind and solar energy on farms

• Coal gradually replaced with cleaner natural gas

• A new generation of nuclear power stations are currently in development

Further reduction of carbon emissions will require some further measures

• More nuclear power stations will be needed to replace existing fossil fuel stations

• A means of storing energy from unreliable sources (such as solar and wind) will need to be developed